Q fever is an understudied infectious disease caused by Coxiella burnetti. Q-Vax, a formalin-inactivated whole bacteria, is currently the only human vaccine approved for Q fever. Attempts have been made to determine the protective epitopes, but such studies have not advanced into an efficacious subunit vaccine. In addition, pre-exposure to C. burnetti, results in adverse reactions to Q-Vax. Given these collective concerns, there is a need to develop an efficacious, preferably subunit vaccine that minimizes such reactivities. The sequencing of C. burnetti genome enables selection of potential vaccine candidates, especially those proteins that are responsible for C. burnetti survival in the host phagolysosome as have similar proteins been identified in other bacteria and subsequently shown to confer protection. Thus, we have identified 68 potential vaccine candidates that will be cloned into eukaryotic expression vectors for DNA vaccination. Using a reductionist approach (Specific Aim 1), candidates will be selected for their ability to reduce infection subsequent to live challenge using the phase I of Nine Mile C. burnetti strain (provided by Core A). In addition, information derived from Projects 1, 2, and 3 will also be used to assist in the selection process. Once candidates are identified, these will be administered to mice and to guinea pigs in suitable combinations with molecular adjuvants to enhance cell-mediated and/or humoral immunity (Specific Aim 2). We hypothesize that we can derive <8 candidates that will be eventually tested in a pneumonic challenge study to determine efficacy of the derived vaccine(s) and a vaccination regimen (Specific Aim 3). Project interactions: This project will be closely integrated with other projects and with Core Facilities described in this proposal. We will work closely with the other investigators in this program project: projects 1,2, and 3.